Inverse Lerp - a super useful yet often overlooked function

Lerp( a, b, t ) = value
InvLerp( a, b, value ) = t

• lerp returns a blend between a and b, based on a fraction t
• inverse lerp returns a fraction t, based on a value between a and b

Use case! ?

Say you want to control audio source volume based on distance

• at 10 meters, you want volume 1
• at 20 meters, you want volume 0

Then the volume is then given by

volume = InvLerp( 20, 10, distance )

If you've ever used photoshop's levels tool, then you've used both lerp and inverse lerp! ?

The input values use inverse lerp, the output values use lerp!

When used with images, inverse lerp can be used to increase value contrast! for example, here's a selfie before and after an inverse lerp?

Also, note that some Lerp/InvLerp functions also extrapolate (such as in shaders), while others clamp the values within your given range (such as Unity's Mathf.Lerp/InverseLerp functions)

Make sure you clamp unless you want to extrapolate ?

Here's an interesting use case!

An inv lerp where a and b are colors and the value parameter is the depth of this water, you can achieve hue-shifting for a color elimination effect by depth?

water.mp4

Addendum - another useful function is Remap!

Remap takes a value within a given input range into a given output range, which is basically a combined inverse lerp and lerp!

Here's the code for all three!

(Also, none of these are clamped - they can all extrapolate)

Enjoyed this quick lesson? Check out Freya's work via the following social platforms:

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Want to read more about Lerp? Freya posted a thread here:

Adapted from the original Twitter thread with kind permission of the original author.

Further reading on GameDev.net: A Brief Introduction to Lerp, by Matt DesLauriers